Two active species of dopamine-beta-hydroxylase (DBH) in whole human serum have been identified and characterized. BIBLIOGRAPHIC REFERENCES: Rosenberg, R.C. and Lovenberg, W.: Active dimers of dopamine-beta-hydroxylase in human serum. Molecular Pharmacology, In press (1977). Kopin, I.J., Kaufman, S., Viveros, H., Jacobowitz, D., Lake, C.R., Ziegler, M.G., Lovenberg, W., and Goodwin, F.K.: Dopamine-beta-hydroxylase: Basic and clinical studies. Combined Clinical Staff Conference at the National Institutes of Health. Ann. Int. Med. 85: 211-223, 1976.